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Hash Iteration

3:41 with Jason Seifer

Hashes have several different ways of iteration -- keys, values, and both keys and values at the same time. Here, we'll learn how to use Ruby to loop through or iterate over a hash, using methods like "each."

Code Samples

The following code samples will use this hash:

business = { "name" => "Treehouse", "location" => "Portland, OR" }

We can work with each key and value using the each method, which takes two arguments. We separate arguments to blocks using a comma, just like method arguments:

business.each do |key, value|
  puts "The hash key is #{key} and the value is #{value}."
end

The each method is aliased as each_pair.

We can iterate over hash keys using the each_key method, which takes one argument:

business.each_key do |key|
  puts "Key: #{key}"
end

The same thing applies to values using the each_value method, which also takes one argument:

business.each_value do |value|
  puts "Value: #{value}"
end

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    Arrays aren't the only Ruby type that get to see the benefits of iteration. 0:00
    In Ruby collections we learned about arrays and hashes. 0:05
    Hashes have several different ways of using iteration. 0:10
    Keys, values, and both keys and values at the same time. 0:14
    Let's take a look at how to iterate over hashes now using workspaces. 0:19
    Using a Ruby workspace, let's go ahead and create a new file. 0:24
    We're gonna call this hash_iteration.rb. 0:28
    And since we're going to be working with a hash to iterate, 0:34
    let's go ahead and create one. 0:38
    And we'll create a hash called, business. 0:40
    The "name" is going to be, "Treehouse". 0:43
    And the "location" is "Portland, OR". 0:48
    We can use the each method to iterate over a hash. 0:54
    So, let's go ahead and try that now. 0:58
    We can say business.each and then we set up our block again. 1:02
    Now when we use the each method and 1:11
    iterate over a hash, it takes two arguments. 1:14
    The key and the value. 1:18
    So we'll say, key and value as the block argument. 1:25
    Just like method arguments, we separate block arguments with a comma. 1:30
    And now let's just print it out. 1:36
    We can say, The hash key is #{key} and 1:38
    the value is #{value}. 1:42
    Let's go ahead and run this and see what happens. 1:49
    And we can see that it prints out. 1:53
    The hash key is name and the value is Treehouse. 1:55
    And then it also does, The hash key is location and the value is Portland, OR. 1:58
    So, the each method will go over each key and value inside of the hash. 2:02
    This method is also called each_pair. 2:08
    So if we run that again, we could see it prints out the same exact thing. 2:14
    I'm gonna take that off and I'm just gonna comment to myself, 2:18
    The each method is also each_pair. 2:26
    We also have ways of iterating over just the keys, so 2:30
    we could say business.each_key. 2:35
    And that will take one argument, since it's just the keys. 2:42
    And let's run that, clear my screen. 2:50
    We get all the keys, and then we can also do that with values. 2:54
    And instead of saying each_key, we do each_value. 3:01
    Once again, this takes one argument. 3:06
    And if I run that again, we'll see it prints out the keys and 3:16
    the values just like in arrays. 3:21
    Any way that we would manipulate these keys and 3:23
    values and items inside of the each method, 3:26
    when iterating over a hash, will not effect the hash itself. 3:30
    Try practicing iterating over hashes now, using workspaces. 3:37

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